Steam strainers for steam turbine plant



April 28, 1964 J. c. LONDON ETAL 3,131,042

STEAM sTRATNERs FOR STEAM TURBTNE PLANT Filed Nov. 28, 1961 2Sheebs--Sheerl 1 JOHN 6 0 M April 28, 1964 J. c. LoNDoN ETAL 3,131,042

STEAM STRAINERS FOR STEAM TURBINE PLANT Filed Nov. 28, 1961 2SheebS-Sheel'. 2

United States Patent G 3,131,042 STEAM STRAINERS FOR STEAM TURBINE PLANTJoseph Clare London, Altrincham, and John Garland, Chadderton, Engiand,assignors to Associated Electrical Industries Limited, London, England,a British company Filed Nov. 28, 1961, Ser. No. 155,395 Claims priority,appiication Great Britain Dec. 22, 1960 it) Claims. (Cl. 55-2'78) Thisinvention relates to steam strainers used to protect steam turbinesagainst the ingress of foreign matter which may be carried through bythe steam coming from the boilers. It applies in particular to the finestrainers used temporarily, during the commissioning period of steamturbine plant. During this period it is customary to iit temporary steamstrainers either to supplement, or in place of, the regular steamstrainers. The temporary units strain to a liner degree than the regularones.

The two most common methods of accommodating the temporary strainers areeither to iit the temporary unit round the regular strainer or, tosubstitute a temporary strainer in place of the regular strainer.

In the iirst case the walls of the temporary strainer are usually thinenough to allow the strainer holes to be punched. These holes aresmaller than the holes in the regular strainer and are pitched tocoincide with the larger holes when the temporary strainer is fittedover the regular one. The temporary unit relies upon the strength of theregular strainer or protection against the crushing eiect caused by thepressure drop through the strainer. This pressure drop increases as theeffective area through the strainer is reduced due to the presence offoreign matter on the inlet side of the strainer.

In the second case the temporary strainer is usually as strong as theregular strainer, the only differences generally being in the size andnumber of strainer holes. In this case, the walls of the temporarystrainer are too thick to allow the strainer holes to be punched.

There is an increasing demand for even finer straining of the steamduring the early life of modern steam plant, but it is diflicult toachieve this with any of the methods in current use. For example, incase (l) the total number of holes in the temporary strainer must be thesame as in the regular strainer. As tbe area through the strainer willvary as the square of the diameter of the strainer holes, the limit onthe size of strainer hole is not due to the difficulty of punching thestrainer holes but rather the severe loss of strainer area that resultsif the holes in the temporary strainer are much smaller than those inthe regular strainer. It has been found that there is a marked loss ofoutput from the turbine plant when temporary strainers of this type areiitted, particularly when the strainer becomes blocked with foreignmatter. It is not considered practicable further to reduce the size ofholes through the temporary strainer.

In case (2), although the number of holes can be increased, it is veryditiicult to drill a large number of small holes through metalthicknesses of the order required or the duty.

The object of the invention is to provide a temporary steam strainerthat will give the tine degree of straining required by modern steamplant, whilst being robust enough to be used for the highest possiblesteam conditions and also alowing for long periods of operation withoutcleaning and with little loss of power output.

The improved steam strainer according to this invention consists of thecombination of a coarse strainer and a relatively ne strainerconcentrically mounted with respect to each other, with an annular gapbetween them to break down the pressure drop through the assembly, thecoarse strainer comprising a rigid cylindrical body having a pluralityof radial holes through the side wall,

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and the fine strainer comprising a series of annular plates separatedaxially from each other by spacers of predetermined thickness.

Normally the coarse strainer will be outside the fine strainer; it mayhe the regular strainer which is to be used with the plant, or it may bespecially made of similar form with holes the same size as the regularstrainer, with the iine strainer assembled within so as to provide aunit that can readily take the place of the regular strainer whenrequired.

According to one embodiment the strainer unit assembly comprises anouter cylinder with a plurality of holes drilled radially therethrough,and an inner platetype strainer consisting of a stack of annular platesthreaded over pillars secured to one end of the outer cylinder, withspacer washers on the pillars between adjacent plates and a cover-platesecured to the pillars at the other end of the cylinder to provide arigid unit. The gap between the two strainers may conveniently be aboutone quarter of the diameter of the holes in the outer cylinder.

In another embodiment particularly suitable for larger sizes of strainer(for example around l2 to 14 inches in diameter) the plates of the nestrainer are made up of four segments jointed at the pillars, with buttjoints between adjacent layers staggered in 45 phases. Preferably theseplates are threaded over eight pillars, each 90 segment having asemicircular recess at each end and a central hole to tit around thepillars. The segments are indented to provide projections on one side ofthe same height as the spacing washers between layers, the indents beingpositioned so that with only one pattern of segment the staggeringthereof around the circumference of the strainer brings the indents inone layer out of line with those in the adjacent layers. Such aconstruction provides a particularly rigid assembly using but onepattern of plate, which is more economical being less wasteful toproduce in large sizes as compared with complete annular plates.

For a clearer understanding of the invention attention is directed tothe following description of the accompany ing drawings, in which:

FIG. 1 is an exploded elevational View showing one construction ofstrainer embodying the invention;

FIG. 2 is a partial plan view illustrating a modified construction; and

FIG. 3 is a developed diagram viewed in the direction of the arrows IIIin FIG. 2.

Referring to FIG. 1 there is shown an outer coarse strainer 1 and aninner concentric fine strainer 2. The strainer 1 comprises a cylindricalbody provided with a large number of radial holes 11 in the usualmanner. The tine strainer 2 is built up of a number of plates 20 whichare threaded over pillars 4 securely fixed to the lower end of thecylinder. Pillars 4 may for example be screwed into tapped holes (notshown) in an internal flange on body 1. Strainer plates 20 are separatedaxially by spacers 5 also threaded on to pillars 4. A closing plate 10is secured on the top of body 1 by nuts or screws 12 engaging the endsof pillars 4 thus making a rugged unit which can readily be substitutedfor a regular strainer in a steam plant. Strainer 2 is mountedconcentrically within strainer 1 and defines an annular gap which breaksdown the pressure drop through the complete assembly. This gap 3 willnormally be about one quarter of the diameter of holes 11.

The construction such as described above is suitable for small sizes ofstrainer and employs complete annular plates for the inner strainer.These are wasteful to produce in larger sizes. FIGS. 2 and 3 illustratea modified structure in which the strainer 2 is composed of segmentalplates instead of complete annuli.

Referring to FIGS. 2 and 3, it is seen that each layer of strainer 2consists of a number of segments located on pillars 4 as in the FIG. 1construction. FIG. 2 shows a 90 segment Ztlb with parts of adjoiningsegments 20a, 20c and three pillars 4 out of a total of eight. Eachsegment has a central perforation and a semicircular recess at eac-h endto fit around the pillars. Specifically segment 20h has a central hole30 and end recesses 3l. In assembly strainer 2, the segments in onelayer are displaced by 45 with respect to the segments of adjacentlayers as is illustrated in FIG. 3 whereon parts of six successivelayers of segments Ztl-25 are shown. It will be seen that segment 2Gb oflayer 20 lits over the middle pillar 4 with its end recesses 31 againstpillars 4 on each side and that the othersides of these pillars occupysimilar recesses in the ends of segments 20a and 20c, the ends of thesegments having butt joints. The segments .2l-25 of successive layersbelow layer 20 are in turn circumferentially displaced by 45; thus thesegments 22, 24 are aligned with segments Ztib, their central holespassing over pillars 4, whilst the segments 21, 23, 25 are in alignmentwith each other with their central holes over pillars 4 and their endsabutting pillars 4, and so on throughout the stack of plates which, asin FIG. l, are separated by spacers 5.

In order to afford support for the layers between pillars 4, 4particularly on large diameter strainers, the segments are indented toprovide projections or dimples 6, 6. As shown in FIG. 3, theseprojections are formed on one side of segments such as 20h to the sameheight as washers S and are off-set from the centre towards the ends ofthe segments. In this way, projections 6 in the odd numbered layers arebrought out of line with those 6 in even layers, as clearly shown inFIG. 3, while using only one pattern of segments for the whole assembly.

It is to be understood that structural modifications may be made withoutdeparting from the scope of the invention. For example, projections mayin some cases be provided on the annular plates 20 of FIG. l, and ineither embodiment such projections may be provided on both sides of theplates or segments. Pillars 4 may be fixed, as by screwing, to a flange13 at the bottom of body 1 (FIG. 2), or to an end plate secured to thebottom of the body in like manner to the top plate shown in FIG. 1.

The fine strainer is normally litted downstream of the coarse strainer,so that the relatively more robust coarse strainer gives a measure ofprotection to the line strainer, and also gives progressively less areathrough the strainer stages as the steam becomes progressively cleaner.If the direction of steam tlow is radially outwards, the tine strainermay be iitted over the outside of the regular strainer.

What we claim is:

1. In a steam turbine, a steam strainer comprising a coarse stage and aline stage each constructed as substantially cylindrical bodiescoaxially arranged with an annular gap therebetween and arranged tocause a generally radial liow of steam directly through said stages inseries without change of llow direction, the coarse stage comprising ahollow cylindrical body with the wall perforated in the radial directionwith holes of diameter of substatnially the order of magnitude of thewall thickness, such wall thickness being capable of withstanding thecrushing effect due to pressure drop in the steam passing through thestrainer, and the iine strainer comprising a stack of annular platesthreaded over a plurality of pillars, spacer washers threaded on thepillars between adjacent plates, and rigid end plates which are securedto both ends of the pillars and hold the plates together as a rigidunit.

2. A steam strainer according to claim 1, wherein said annular strainerplates are each composed of a plurality of arcuate segments with buttjoints at each end of said segments.

3. A steam strainer according to claim 2, wherein said strainer platesare assembled on said pillars with the segments of each layer displacedcircumferentiallyV with respect to the segments in adjacent layers.

4. A steam strainer according to claim 3, wherein said segments areprovided with projections on at least one side face, said projectionsextending to the same height as the spacing members between adjacentlayers of segments.

5. A steam strainer according to claim 4, wherein said projections areoiset from the centre towards the ends of said segments, whereby theprojections in one layer of plates are brought out of line with theprojections in adjacent layers of plates.

6. A steam strainer according to claim 1, wherein said pillars arerigidly mounted radially inward of said cylindrical side wall, the lowerend of said wall being provided with an internal liange, means fixingsaid pillars to said flange, and means including a closing plate securedto the top of said wall and engaging the upper ends of said pillars.

7. A steam strainer according to claim 6, wherein said annular strainerplates are each composed of a plurality of arcuate segments with buttjoints at their ends, said segments being assembled on said pillars withthe joints in each layer of plates displaced circumferentially withrespect to the joints in adjacent layers of plates.

8. A steam strainer according to claim 7, wherein said segments areperforated at the middle to enable them to pass over one of saidpillars, and the ends of said segments are formed with recesses which inassembled condition t around the pillars on each side of said onepillar.

9. A steam strainer according to claim 8, wherein said segments areprovided with projections on at least one side face, said projectionsextending to the same height as the spacing members between adjacentlayers of segments.

10. A steam strainer according to claim 9, wherein said projections areoiset from the centre towards the ends of said segments whereby theprojections in one layer of plates are brought out of line with theprojections in adjacent layers of plates.

References Cited in the le of this patent UNITED STATES PATENTS2,330,945 Becker Oct. 5, 1943 2,670,851 Curtis Mar. 2, 1954 FOREIGNPATENTS 642,937 Great Britain Sept. 13, 1950 535,492 Canada Ian. 8, 1957773,875 Great Britain May 1, 1957

1. IN A STEAM TURBINE, A STEAM STRAINER COMPRISING A COARSE STAGE AND AFINE STAGE EACH CONSTRUCTED AS SUBSTANTIALLY CYLINDRICAL BODIESCOAXIALLY ARRANGED WITH AN ANNULAR GAP THEREBETWEEN AND ARRANGED TOCAUSE A GENERALLY RADIAL FLOW OF STEAM DIRECTLY THROUGH SAID STAGES INSERIES WITHOUT CHANGE OF FLOW DIRECTION, THE COARSE STAGE COMPRISING AHOLLOW CYLINDRICAL BODY WITH THE WALL PERFORATED IN THE RADICALDIRECTION WITH HOLES OF DIAMETER OF SUBSTANTNIALLY THE ORDER OFMAGNITUDE OF THE WALL THICKNESS, SUCH WALL THICKNESS BEING CAPABLE OFWITHSTANDING THE CRUSHING EFFECT DUE TO PRESSURE DROP IN THE STEAMPASSING THROUGH THE STRAINER, AND THE FINE STRAINER COMPRISING A STACKOF ANNULAR PLATES THREADED OVER A PLURALITY OF PILLARS, SPACER WASHERSTHREADED ON THE PILLARS BETWEEN ADJACENT PLATES, AND RIGID END PLATESWHICH ARE SECURED TO BOTH ENDS OF THE PILLARS AND HOLD THE PLATESTOGETHER AS A RIGID UNIT.